Not knowing this topic I'd the norm! Schools do not teach the actual political context in these countries, it is all filtered through simplistic narratives that were crafted by anticommunist propagandists (McCarthyites, e.g.) that wanted to thread the needle of presenting Nazis as people to be opposed without giving socialists the credit for doing 80% of the opposing. And the issues related to capitalism are glossed over at all costs because, of course, those same writers (1) are big fans of capitalism while (2) not understanding it very well themselves. The most powerful tool in propaganda is emphasis. To take a topic and seemingly discuss it while neglecting inconvenient aspects and nailing the ones you care about. We are constantly bombarded with this exact form of propaganda, it has become self-sustaining. People don't even know they're doing it, the narratives have calcified.

And then, shock! They open up a history book, they read the old German papers, they see the Soviet Archives, and the realities disagree almost completely with what the Texas Board of Education approved textbook said.

Anyways, give yourself a break, none if us are immune to propaganda. Just keep that spark of humility alive and read thoroughly. I recommend reading critical materials, like media criticism and left theory and histories, as these provide very useful tools for tackling mainstream sources critically.

If you would like a (short) book recommendation, you might appreciate Blackshirts and Reds by Michael Parenti, which actually covers the exact topic of fascists vs. socialists from a critical historical perspective.